When uploading items to a Distribution/Supplier account, Jellyfish asks you for a "Category". This is a number that will categorize your item in Jellyfish. For example, the category number for "Beer" is "1".
When you upload a CSV with multiple items, the categories will need to be listed numerically; otherwise, your upload will result in an error which is explained in this article.
In order for all Distributors and Suppliers to use the same category ID, categories are managed by Jellyfish. If you wish to upload a CSV but are unsure about the categories, open a support ticket.